Rosie McDonnell has suffered a tear to her medial collateral ligament.
The Pompey defender suffered the injury against Crawley Wasps in the Blues' last match before the season was suspended.
She is currently undergoing scans and treatment, so the club can not yet confirm how long she will be on the sidelines.
"We obviously don’t know when she will be able to return, but in the meantime, the club will continue to support her through the recovery phase.
"Not only will she be a big loss on the pitch, as she offers us so much at both ends, but her infectious character in the dressing room at training will be missed too."